The long-term objective of this research is to understand how bovine leaukemia virus (BLV) induces malignancy in its target cells. The specific aims of this proposal are to induce transformation by BLV of hematopoietic cells in vitro, to assess the state of BLV infection in the transformed cells and to characterize the hematopoietic lineage of the transformed cells. BLV is a naturally occurring retrovirus that causes lymphoid cancer in cattle long after infection. The mechanism of tumorigenesis is unknown; BLV does not contain a cell-derived oncogene and does not promote the expression of cellular oncogenes by promoter insertion. These are also characteristics of human T cell leukemia virus (HTLV I). BLV and HTLV I are genetically similar and there are striking parallels in the epidemiologies and the pathogenesis of the diseases caused by these viruses, although HTLV induces T cell disease whereas BLV is thought to induce B cell disease. It is important to understand BLV infection and tumorigenesis in detail because this knowledge will be valuable for designing treatment and preventive measures for HTLV I-induced lymphoma. A cell culture system in which BLV transforms target cells is needed to study the cellular and molecular events leading to transformation. Complex cell cultures prepared from hematopoietic tissues of cows and sheep will be infected by BLV. The tissues are selected because they contain cells in different stages of B- and T- cell differentiation. Conditioned media containing growth factors for lymphoid cells will be used to stimulate mitosis in the cultures. The populations of continuously dividing cells that result from BLV infection will be examined for their content of viral DNA and RNA and for their expression of viral proteins by molecular hybridization and by immunoenzymatic staining. The lymphoid lineage of the transformed cells will be identified by immunofluorescent and immunoenzymatic staining for markers expressed by cow or sheep B and T lymphocytes.